A desktop alignment platform for an extreme ultraviolet coaxial optical system and a method thereof

Abstract

The application discloses a desktop type adjusting platform for an extreme ultraviolet coaxial optical system and a method thereof, and belongs to the field of precise adjusting devices of optical systems. The adjusting platform comprises an optoelectronic autocollimator, a motorized turntable, an image acquisition module, a light source and a mirror group adjusting mechanism. The optical axis of the optoelectronic autocollimator coincides with the rotation shaft of the motorized turntable and serves as the reference axis of the adjusting platform. The motorized turntable is fixed on an optical platform. A plane mirror is fixed on the surface of the motorized turntable. The optoelectronic autocollimator is arranged on one side of the plane mirror. The image acquisition module is arranged between the plane mirror and the optoelectronic autocollimator. The conventional adjusting scheme is limited in application to optical systems, and lacks flexibility and integration. The adjusting platform is a complete and independent system, integrates light path calibration, attitude control and image analysis units, does not need external auxiliary equipment, can be flexibly arranged according to the aperture and object image relationship of the optical system to be adjusted, and realizes rapid adaptive precise adjustment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical system precision assembly and adjustment device, and particularly relates to a desktop assembly and adjustment platform for an extreme ultraviolet coaxial optical system and a method thereof. BACKGROUND

[0002] The extreme ultraviolet waveband (10-124 nm) covers the main atomic resonance lines and absorption edges of most low and medium atomic number elements, so that the extreme ultraviolet optical technology has important application value in the fields of chemical element analysis, plasma diagnosis, biological microscopic imaging, space astronomical observation and extreme ultraviolet lithography. Since all materials have strong absorption in this waveband, a transmissive optical system cannot work, and a reflective system based on multilayer film mirrors must be used. Among them, the coaxial reflective optical system has the characteristics of good symmetry, small aberration, compact structure and high resolution, and becomes the mainstream technical scheme, and a typical representative is the Schwarzschild structure. However, in order to realize ideal imaging or accurate focusing, the mirrors of this kind of system must be strictly coaxial and the mirror spacing must be accurately controllable, and any slight tilt, eccentricity or spacing error will introduce an aberration that is difficult to compensate, so high requirements are put forward for the assembly and adjustment precision. The traditional assembly and adjustment method relies on fixed devices and external separate equipment, and the operation is complex and flexible, which is difficult to meet the high-efficiency and high-precision assembly and adjustment requirements of different specifications of extreme ultraviolet coaxial systems.

[0003] The assembly and adjustment of the existing extreme ultraviolet coaxial optical system (such as the Schwarzschild system) mainly relies on a centering instrument to adjust the center deviation of each optical element. However, this method has obvious limitations: on the one hand, it cannot effectively monitor and calibrate the key parameter of mirror spacing; on the other hand, when the curvature radius of the mirror to be assembled and adjusted is too large or too small, it is difficult to make the convergence point of the centering instrument and the curvature center of the mirror surface accurately coincide in a limited space, resulting in a decrease in assembly and adjustment precision or even failure. Therefore, the traditional centering instrument scheme has insufficient applicability to optical systems with special numerical aperture or extreme mirror curvature, which limits its application in high-precision and diversified extreme ultraviolet optical assembly and adjustment. SUMMARY

[0004] The purpose of the present application is to provide a desktop assembly and adjustment platform for an extreme ultraviolet coaxial optical system and a method thereof to solve the problems mentioned in the background.

[0005] In order to achieve the above object, the application provides a desktop adjustment platform for an extreme ultraviolet coaxial optical system, comprising a photoelectric autocollimator, a motorized turntable, an image acquisition module, a light source and a mirror group adjustment mechanism, the optical axis of the photoelectric autocollimator coincides with the rotation axis of the motorized turntable and serves as a reference axis of the adjustment platform, the motorized turntable is fixed on an optical platform, a plane mirror is fixed on the surface of the motorized turntable, the photoelectric autocollimator is arranged on one side of the plane mirror, the image acquisition module is arranged between the plane mirror and the photoelectric autocollimator, the light source is located at a target object distance on the reference axis, and the mirror group adjustment mechanism is fixedly connected with the surface of the motorized turntable and stably rotates together with the motorized turntable.

[0006] Preferably, the mirror group adjustment mechanism is a combination of a high-precision three-axis displacement table, a pitch table and an arc swing table.

[0007] Preferably, the extreme ultraviolet coaxial optical system is composed of a series of extreme ultraviolet multilayer film mirrors, the reflecting surfaces of all the mirrors are symmetrical to the optical axis of the system, and the vertex normal lines of all the optical elements coincide with the optical axis of the extreme ultraviolet coaxial optical system.

[0008] Preferably, the mirror group adjustment mechanism is fixedly connected with the surface of the motorized turntable and stably rotates together with the motorized turntable.

[0009] Preferably, the light source is a visible light source or an extreme ultraviolet light source matched with the optical system.

[0010] Preferably, the image acquisition module is an industrial camera matched with the wave band of the light source.

[0011] The application further provides an adjustment method, the reference axis of the adjustment platform is established by means of self-collimation adjustment, and the method comprises the following steps:

[0012] S1, fixing the motorized turntable, installing a plane mirror on the surface of the motorized turntable, marking a mark point on the surface of the plane mirror for indicating the center of the turntable, and making the reflecting surface of the plane mirror parallel to the mounting surface of the motorized turntable;

[0013] S2, adjusting the photoelectric autocollimator to a first working distance to make the photoelectric autocollimator emit collimated light, adjusting the pitch and yaw angles of the photoelectric autocollimator, and making the cross-shaped wire image received by the photoelectric autocollimator and reflected by the plane mirror coincide with the reference cross-shaped wire built in the photoelectric autocollimator;

[0014] S3, adjusting the photoelectric autocollimator to a second working distance to make the photoelectric autocollimator clearly image on the surface of the plane mirror, adjusting the horizontal and vertical positions of the photoelectric autocollimator, and making the mark point image on the surface of the plane mirror coincide with the reference cross-shaped wire built in the photoelectric autocollimator;

[0015] S4, rotate the electric rotary table for one circle, and switch the working distance of the photoelectric autocollimator between the first working distance and the second working distance alternately, fine-tune the attitude and position of the photoelectric autocollimator, until the cross-shaped wire image reflected by the plane mirror and the mark point image on the surface of the photoelectric autocollimator are always coincident with the reference cross-shaped wire at any angle, at this time, the optical axis of the photoelectric autocollimator is coincident with the rotation axis of the electric rotary table, and thus the establishment of the reference axis of the platform is completed.

[0016] Preferably, the optical axis of the extreme ultraviolet coaxial optical system is adjusted by the mirror group adjustment mechanism until it is coincident with the reference axis of the platform, and the adjustment precision is judged by the electric rotary table and the image acquisition module.

[0017] Preferably, the adjustment method of the light source is that the photoelectric autocollimator is focused to the target working distance, the light source is adjusted until the center of the light outlet of the light source is coincident with the reference cross-shaped wire built in the photoelectric autocollimator.

[0018] Therefore, the desktop type platform for the extreme ultraviolet coaxial optical system and the method thereof have the following beneficial effects:

[0019] 1. High precision and comprehensiveness: the present application can realize the precise adjustment and verification of the coaxial precision and the mirror spacing of the extreme ultraviolet coaxial optical system at the same time by establishing a high-precision reference axis and combining the autocollimator and image analysis, and overcomes the defect that the traditional method can only adjust the center deviation.

[0020] 2. High flexibility and versatility: the platform can be configured with light sources and cameras of different wavebands, which can be used for safe and convenient initial adjustment by visible light, and final verification by extreme ultraviolet light, and is suitable for a wide range of applications; compared with the traditional centering instrument scheme which is not suitable for optical systems with special numerical aperture or extreme mirror curvature, the present application scheme can be flexibly adapted to various optical systems with different numerical apertures and object-image relationships, and breaks through the limitation of traditional equipment on special curvature mirrors.

[0021] 3. High integration and convenience: all functional units required for adjustment are highly integrated in an independent system, without the need for external auxiliary equipment, which realizes rapid deployment and precise adjustment in a standard laboratory, greatly improves the adjustment efficiency and the convenience of operation.

[0022] The technical solutions of the present application will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of an extreme ultraviolet focusing Schwarzschild system;

[0024] Figure 2 It is a schematic diagram of the reference axis establishment method of the adjustment platform;

[0025] Figure 3 The monitoring and shooting picture of photoelectric autocollimator for establishing process of platform reference axis;

[0026] Figure 4 The schematic diagram for assembling and adjusting the extreme ultraviolet focusing Schwarzschild system of the platform;

[0027] Figure 5 The focusing result shooting picture of the Schwarzschild system;

[0028] Reference numerals

[0029] 1, light source; 2, secondary mirror; 3, primary mirror; 4, focal spot; 5, motorized turntable; 6, plane mirror; 7, photoelectric autocollimator; 8, reference axis; 9, visible light CCD; 10, lens barrel; 11, three-dimensional adjustment frame. DETAILED DESCRIPTION

[0030] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will combine the drawings in the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0031] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0032] For the precise assembly and adjustment requirement of the extreme ultraviolet coaxial optical system, the present application provides a desktop assembly and adjustment platform for the extreme ultraviolet coaxial optical system, which comprises a photoelectric autocollimator 7, a motorized turntable 5, an image acquisition module, a light source 1 and a mirror group adjustment mechanism. The optical axis of the photoelectric autocollimator 7 coincides with the rotation axis of the motorized turntable 5 and serves as a reference axis 8 of the assembly and adjustment platform. The motorized turntable 5 is fixed on an optical platform, and a plane mirror 6 is fixed on the surface of the motorized turntable 5. The photoelectric autocollimator 7 is arranged on one side of the plane mirror 6, and the image acquisition module is arranged between the plane mirror 6 and the photoelectric autocollimator 7. The mirror group adjustment mechanism is a combination of a high-precision three-axis displacement table, a pitch table and an arc swing table, and the extreme ultraviolet coaxial optical system can be adjusted in various angles through the mirror group adjustment mechanism.

[0033] The extreme ultraviolet coaxial optical system is composed of a series of extreme ultraviolet multilayer film mirrors, the reflecting surfaces of all the mirrors are symmetrical to the optical axis of the system, and the vertex normal lines of all the optical elements coincide with the optical axis of the extreme ultraviolet coaxial optical system.

[0034] The light source 1 is located at the target object distance on the reference axis 8.

[0035] The mirror group adjusting mechanism is fixedly connected with the surface of the motorized turntable 5 and can stably rotate together with the motorized turntable 5.

[0036] The light source 1 is a visible light source or an extreme ultraviolet light source matched with the optical system; and the image acquisition module can selectively use an industrial camera matched with the wave band of the light source 1.

[0037] The “desktop type” is defined as follows: the platform is a complete and independent adjustment platform integrating all the required functional units such as optical path calibration, attitude control and image analysis, does not need external auxiliary equipment, and can be flexibly arranged in a laboratory according to the aperture and object-image relationship of the extreme ultraviolet optical system to be adjusted, so as to realize rapid adaptive precise adjustment.

[0038] The application further provides an adjustment method, and the reference axis 8 of the adjustment platform is established by a self-collimation adjustment mode, and the method comprises the following steps:

[0039] S1, fix the motorized turntable 5, install a plane mirror 6 on the surface of the motorized turntable 5, the plane mirror 6 is marked with an identification point for indicating the center of the turntable, and the reflecting surface of the plane mirror 6 is parallel to the mounting surface of the motorized turntable 5;

[0040] S2, focus the photoelectric autocollimator 7 to a first working distance (A) to make it emit collimated light, adjust the pitch and yaw angles of the photoelectric autocollimator 7, so that the cross-shaped wire image received by the photoelectric autocollimator 7 and the cross-shaped wire image reflected by the plane mirror 6 are coincident with the reference cross-shaped wire built-in the photoelectric autocollimator 7;

[0041] S3, focus the photoelectric autocollimator 7 to a second working distance (B) to make it clearly image on the surface of the plane mirror 6, adjust the horizontal and vertical positions of the photoelectric autocollimator 7, so that the identification point image on the surface of the plane mirror 6 and the reference cross-shaped wire built-in the photoelectric autocollimator 7 are coincident;

[0042] S4, rotate the motorized turntable 5 for one revolution, and alternately switch the working distance of the photoelectric autocollimator 7 between the first working distance A and the second working distance B, and finely adjust the attitude and position, until the cross-shaped wire image reflected by the plane mirror 6 and the identification point image on the surface of the plane mirror 6 are always coincident with the reference cross-shaped wire at any rotation angle, at this time, the optical axis of the photoelectric autocollimator 7 coincides with the rotation axis of the motorized turntable 5, and thus the reference axis 8 of the adjustment platform is established.

[0043] The optical axis of the extreme ultraviolet coaxial optical system is adjusted by a mirror group adjustment mechanism until it coincides with the adjustment platform reference axis 8, and the adjustment precision is determined by the motorized turntable 5 and the image acquisition module.

[0044] The adjustment method of the light source 1 is as follows: the photoelectric autocollimator is focused to the target working distance, the light source 1 is adjusted until the center of the light outlet coincides with the reference cross hair inside the photoelectric autocollimator 7.

[0045] Embodiment 1

[0046] This embodiment takes an extreme ultraviolet focusing Schwarzschild system as an example, which is adjusted by the adjustment platform. The Schwarzschild system is a typical extreme ultraviolet coaxial optical system, which realizes focusing or magnification imaging by using a two-mirror reflection structure. As shown in Figure 1 , the optical system includes a primary mirror 3 and a secondary mirror 2 arranged on one side of the primary mirror 3. The primary mirror 3 is a convex spherical mirror, and the secondary mirror 2 is a central aperture concave spherical mirror. The curvature centers and geometric centers of the primary mirror 3 and the secondary mirror 2 are collinear, forming the system optical axis. The incident light is reflected by the primary mirror 3 and the secondary mirror 2 in turn, and focused at the back of the primary mirror 3.

[0047] The specific optical structure parameters of the adjustment platform in this embodiment are shown in Table 1.

[0048] Table 1 Specific optical structure parameters of the adjustment system

[0049]

[0050] The optical system is a focusing Schwarzschild structure with a scaling ratio of 150 times, that is, a 3mm aperture light source can be focused to a 20μm focal spot. The system works in the 13.5nm extreme ultraviolet band, and the primary mirror 3 and the secondary mirror surface are coated with Mo / Si multilayer film. Due to the extremely high scaling ratio of the system, the adjustment tolerance is strict: the adjustment precision of the distance between the two mirrors and the image distance needs to reach the micron level, and the eccentricity of each mirror needs to reach the sub-micron level. The adjustment platform of the present application is designed to meet the high-precision adjustment requirements, and realizes fast and precise adjustment.

[0051] The establishment method of the reference axis 8 is shown in Figure 2 . First, the motorized turntable is fixed on the optical platform through a support, and a plane mirror 6 marked with a motorized turntable center mark is closely attached to the surface of the motorized turntable. The photoelectric autocollimator 7 is placed towards the plane mirror surface. The reference axis 8 is established as follows: first, the photoelectric autocollimator 7 is focused to the first working distance (outgoing parallel light), and the pitch and yaw adjustment knobs are adjusted so that the cross hair image reflected by the plane mirror 6 coincides with the center of the reference cross hair inside the photoelectric autocollimator 7, as shown in Figure 3(a), at this time the collimator optical axis is parallel to the normal of the mirror, i.e. parallel to the rotation axis of the turntable. Then, the photoelectric autocollimator 7 is adjusted to the second working distance (aligned to the surface of the mirror), and the horizontal and vertical positions are adjusted through the three-dimensional adjusting frame 11 placed under the photoelectric autocollimator 7 until the mark point image on the surface of the plane mirror 6 is coincident with the center of the reference cross wire, as shown in Figure 3 (b). Finally, the electric turntable 5 is rotated for one round, and the working distance of the photoelectric autocollimator 7 is alternately switched between the above two states, and the returned cross wire image and the mark point image are always coincident with the built-in reference cross wire, which indicates that the optical axis of the photoelectric autocollimator 7 is coincident with the rotation axis of the electric turntable at this time, and the coincident axis is the reference axis 8 of the assembling platform.

[0052] The plane mirror 6 is removed, and the center of the electric turntable 5 is made to be light transmitting. The photoelectric autocollimator 7 is adjusted to the target object distance, and a LED light source with an aperture of 2.5 mm is placed at the position; according to the theoretical calculation of the Schwarzschild system, the size of the focal spot 4 is 16.7 μm. The mirror barrel 10 of the built-in primary mirror 3 and secondary mirror 2 is installed on the surface of the electric turntable 5, wherein the primary mirror 3 and the secondary mirror 2 are in a spatial free state. The primary mirror 3 is adjusted in position and posture through the three-dimensional adjusting frame 11 rigidly connected with the electric turntable 5; and the secondary mirror 2 is finely adjusted through the bolt top-pulling mechanism on the side wall of the mirror barrel 10. A visible light CCD 9 (i.e. image acquisition module) is placed between the electric turntable 5 and the photoelectric autocollimator 7, so that the photosensitive surface is coincident with the theoretical image point of the system. The measurement and calibration of all axial distances are realized through the photoelectric autocollimator 7. At this time, the layout of the assembling platform is prepared, and the overall arrangement is shown in Figure 4

[0053] During the assembling process, the focusing light spot is monitored in real time through the visible light CCD 9, the CCD pixel size used is 2.2 μm, the postures of the primary mirror and the secondary mirror 2 and the distance between the two mirrors are adjusted until the focusing light spot on the CCD is smallest, the electric turntable 5 is rotated, and at the same time, it is judged whether the light spot moves or is out of focus. If the light spot moves or is out of focus, it indicates that the mirror centers of the two mirrors are not adjusted to be coincident with the reference axis 8, and the adjustment is further made according to the light spot during the rotation. Until the electric turntable 5 is rotated and the focal spot 4 is always smallest and does not move, the assembling is completed. Figure 5 The result of the assembled focal spot 4 is that the diameter of the focal spot 4 is about 7-8 pixels, i.e. the actual size of the focal spot 4 is 15.4 μm-17.6 μm, which is consistent with the theory, and the position of the focal spot 4 is unchanged by using the turntable rotating objective lens group, and the assembling is completed.

[0054] ​During the alignment process, the shape of the focused spot output by the real-time monitoring system is monitored by the visible light CCD 9, and the pixel size of the CCD is 2.2 μm. By adjusting the attitude of the primary and secondary mirrors 2 and precisely controlling the distance between the two mirrors, the spot size in the field of view of the CCD is gradually optimized until it is the smallest. Subsequently, the motorized turntable 5 is rotated for one revolution, and the change of the spot during rotation is observed. If the spot appears to be drifting or out of focus, it indicates that the coaxial state of the optical mirror group has not been completely established, and the mirror center has not been precisely aligned with the reference axis 8. The mirror group attitude needs to be iteratively fine-tuned according to the direction of the spot shift and the degree of defocus. Finally, when the motorized turntable 5 is rotated within a range of 360°, the focal spot 4 always maintains the smallest size and stable position without movement, which means that the alignment of the system is completed. Figure 5 The image of the focal spot 4 collected after the alignment is shown, and its diameter is about 7-8 pixels, corresponding to an actual size of 15.4 μm-17.6 μm, which is in good agreement with the theoretical design value (16.7 μm). Further rotation of the motorized turntable 5 verifies that the position of the focal spot 4 does not shift at all, which fully proves the alignment accuracy and stability, indicating that the entire alignment process is completed.

[0055] Therefore, the desktop alignment platform for an extreme ultraviolet coaxial optical system and the method thereof according to the present application highly integrate all functional units required for alignment into a single independent system, without the need for external auxiliary equipment, realize rapid deployment and precise alignment in a standard laboratory, and greatly improve the alignment efficiency and operational convenience.

[0056] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can still be modified or replaced by equivalents, and these modifications or replacements should not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A desktop alignment platform for an extreme ultraviolet coaxial optical system, characterized by: The system includes an opto-autocollimator, an electric turntable, an image acquisition module, a light source, and a lens adjustment mechanism. The optical axis of the opto-autocollimator coincides with the rotation axis of the electric turntable and serves as the reference axis for the assembly and adjustment platform. The electric turntable is fixed on the optical platform, and a plane mirror is fixed on the surface of the electric turntable. The opto-autocollimator is located on one side of the plane mirror, and the image acquisition module is located between the plane mirror and the opto-autocollimator. The light source is located at the target object distance on the reference axis. The lens adjustment mechanism is fixedly connected to the surface of the electric turntable and rotates stably together with the electric turntable. The reference axis of the assembly and adjustment platform is established through a self-collimation assembly and adjustment method, including the following steps: S1. Fix the electric turntable and install a plane reflector on the surface of the electric turntable. The surface of the plane reflector is engraved with markings to indicate the center of the turntable, and the reflective surface of the plane reflector is parallel to the mounting surface of the electric turntable. S2. Focus the photoelectric autocollimator to the first working distance so that the photoelectric autocollimator emits collimated light. Adjust the pitch and yaw angles of the photoelectric autocollimator so that the crosshair image received by the photoelectric autocollimator and reflected back by the plane mirror coincides with the reference crosshair built into the photoelectric autocollimator. S3. Focus the photoelectric autocollimator to the second working distance so that the photoelectric autocollimator can clearly image the plane mirror surface. Adjust the horizontal and vertical positions of the photoelectric autocollimator so that the marked point image on the plane mirror surface coincides with the reference crosshairs built into the photoelectric autocollimator. S4. Rotate the electric turntable one revolution and alternately switch the working distance of the photoelectric autocollimator between the first working distance and the second working distance. Fine-tune the attitude and position of the photoelectric autocollimator until, at any angle, the crosshair image reflected back by the plane mirror and the image of the marked point on the surface of the photoelectric autocollimator always coincide with the reference crosshair. At this time, the optical axis of the photoelectric autocollimator coincides with the rotation axis of the electric turntable, and the reference axis of the assembly and adjustment platform is established.

2. The desktop alignment platform for an EUV coaxial optical system according to claim 1, characterized in that: The mirror assembly adjustment mechanism is a combination of a high-precision three-axis displacement stage, a pitch stage, and an arc swing stage.

3. The desktop alignment platform for an EUV coaxial optical system according to claim 1, wherein: The extreme ultraviolet coaxial optical system consists of a series of extreme ultraviolet multilayer mirrors. The reflecting surfaces of all mirrors are symmetrical about the optical axis of the system, and the vertex normals of all optical elements coincide with the optical axis of the extreme ultraviolet coaxial optical system.

4. The desktop alignment platform for an EUV coaxial optical system according to claim 1, wherein: The light source is a visible light source or an extreme ultraviolet light source matched with the optical system.

5. The desktop alignment platform for an EUV coaxial optical system according to claim 1, wherein: The image acquisition module is an industrial camera that matches the wavelength of the light source.

6. An assembly and adjustment method, applied to a desktop assembly and adjustment platform for an extreme ultraviolet coaxial optical system as described in any one of claims 1-5.

7. A method of assembling according to claim 6, wherein: The optical axis of the extreme ultraviolet coaxial optical system is adjusted by the lens assembly adjustment mechanism until it coincides with the reference axis of the assembly platform. The accuracy of the assembly is determined by the electric turntable and the image acquisition module.

8. A method of assembling according to claim 7, wherein: The method for adjusting the light source is as follows: focus the photoelectric autocollimator to the target working distance, and adjust the light source until the center of the light source's output port coincides with the reference crosshairs built into the photoelectric autocollimator.

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